Gliederung

Background: Concurrent chemoradiation is standard therapy for head and neck malignancies despite high rates of normal tissue toxicity. Furthermore, good treatment responses often result in rapid tumor shrinkage that markedly alter head and neck anatomy. Standard practice does not account for this and can lead to overtreatment of normal tissue and undertreatment of tumor. Pilot studies have used adaptive photon IMRT (ART), re-simulating patients during therapy and modifying target volumes and plans, to try to adapt therapy to these changes. We propose that proton therapy for head and neck tumors may provide a better toxicity profile and tumor coverage than photon therapy, with or without adaptive therapy.

Methods: CT images from 5 patients who required re-simulation during their course of standard irradiation were used to quantify dosimetric differences between photon and proton therapy. Planning tumor volumes (PTVs) and normal tissue structures (parotids, larynx, spinal cord, brainstem, mandible) were contoured on the initial and re-simulation CT. Three plans were generated for each patient: IMRT photon, ART photon, and proton plans using the initial CT. Dose volume histograms were generated to compare doses to tumor and normal structures.

Conclusions: Proton therapy has a more favorable toxicity profile than either standard IMRT or adaptive radiotherapy with IMRT especially with respect to the spinal cord, brainstem and left and right parotid glands. In this study, adaptive radiotherapy did not prove to be significantly better than standard IMRT despite smaller target volumes. With larger study population set, longitudinal studies may prove that proton therapy is superior to decrease normal tissue toxicity while still providing full coverage to the tumor and PTVs.